Variable discharge pump

ABSTRACT

A variable discharge pump is provided, the pump comprising a pumping chamber and a reciprocating plunger disposed within a plunger bore so as to reciprocate within the pumping chamber. The pump also has an electrically actuated spill control valve which opens or closes fluid communication between the pumping chamber and a low pressure area. The control valve is operated for a first period of time extending from a first time point occurring after the plunger passes bottom dead center to a second time point occurring before the plunger passes top dead center. The control valve is then operated for a second period of time extending from a third time point occurring between the second time point and the passing of the plunger through top dead center to a fourth time point occurring after the plunger has passed top dead center.

TECHNICAL FIELD

The present invention relates to the field of variable discharge pumps.Particularly, though not exclusively, the invention relates to avariable discharge pump suitable for pumping fuel into the common railof a common rail fuel injection system.

BACKGROUND

The present invention relates to the field of variable discharge pumps.Particularly, though not exclusively, the invention relates to avariable discharge pump suitable for pumping fuel into the common railof a common rail fuel injection system.

Each downward stroke of the plungers feeds fuel from the fuel feed portinto the pumping chamber. When the control valve member is open, thefuel passes through the valve and back to the feed port via the returnpassage when the plungers move upward. When pressurized fuel is to befed into the common rail, a control pulse moves the control valve memberinto the closed position. At the same time, the plunger is undertakingan upward stroke. Because the control valve is closed, pressurization ofthe fuel takes place in the pumping chamber. When the fuel pressurereaches a certain level, the discharge valve opens and the pressurizedfuel passes from the pumping chamber into the common rail. Theconsequent drop in fuel pressure in the pumping chamber allows the valvespring to push the control valve member into its open position,whereupon it comes into contact with a valve stop.

In order to maintain fuel pressure in the common rail, the controlvalves in the pump are required to very frequently pressurize fuel inthe pumping chambers. For each rotation of the pump camshaft, eachcontrol valve will be required to pressurize fuel several timesdepending upon the number of lobes on the cam. This means that thecontrol valve member is being energized and de-energized extremelyfrequently. Every time that the valve member is de-energized, it impactsthe valve seat under the action of the spring. Over a long period oftime, this impact between the valve member and valve seat may damage thevalve member. This may lead to a shortening of valve life anddeterioration of the seal effected by the valve member when closed. Suchseal deterioration may lead to variation in fuel pressure in the pumpingchamber and consequent variation in overall pump performance.

It is an aim of the present invention to obviate or mitigate one or moredisadvantages associated with prior art devices and methods.

SUMMARY OF THE INVENTION

According to a first aspect of the invention, there is provided a pumpcomprising a first pumping chamber and a first reciprocating plungerdisposed within a first plunger bore so as to reciprocate within thefirst pumping chamber. The pump includes a first electrically actuatedspill control valve adapted to open or close fluid communication betweenthe first pumping chamber and a low pressure area. The pump alsoincludes a controller adapted to operate the first control valve for afirst period of time extending from a first time point occurring afterthe first plunger passes bottom dead center to a second time pointoccurring before the first plunger passes top dead center. Thecontroller may also be adapted to operate the control valve for a secondperiod of time extending from a third time point occurring between thesecond time point and the passing of the first plunger through top deadcenter to a fourth time point occurring after the first plunger haspassed top dead center.

According to a second aspect of the present invention, there is providedan internal combustion engine including a pump according to the firstaspect of the present invention.

According to a third aspect of the present invention, there is provideda method of pressurizing fluid in a pump, the method comprising thesteps of supplying low pressure fluid to a pumping chamber andreciprocating a plunger within the pumping chamber so as to force fluidfrom the pumping chamber. The fluid may be returned from the pumpingchamber through an electrically actuated spill control valve. Thecontrol valve may be operated to pressurize the fuel in the pumpingchamber during a forward stroke of the plunger. The pressurized fuel maybe discharged through a discharge port in communication with the pumpingchamber. The operating step may include operating the control valve fortwo separate periods of time, a first period of time extending from afirst time point occurring after the plunger passes bottom dead centerto a second time point occurring before the plunger passes top deadcenter, and a second period of time extending from a third time pointoccurring between the second time point and the passing of the plungerthrough top dead center to a fourth time point occurring after theplunger has passed top dead center.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a common rail fuel injectionsystem;

FIG. 2 is a front sectioned view of a variable discharge pump suitablefor use in the injection system of FIG. 1;

FIG. 3 is a side sectioned view of the pump of FIG. 2;

FIG. 4 is a detail view taken from the side view of FIG. 3 showing thecontrol valve of the pump; and

FIG. 5 is a chart illustrating the operation of a spill control valveforming part of the pump of FIGS. 2-4.

DETAILED DESCRIPTION

Referring to FIG. 1, a fuel system, generally designated 10, is shown.The system 10 includes a number of fuel injectors 22, each of which isconnected to a high pressure fuel rail 20 via a respective branchpassage 21. The fuel rail 20 is supplied with high pressure fuel from avariable discharge pump 16 which receives low pressure fuel from a fueltank 12 via a fuel transfer pump 14. The fuel tank 12 is also connectedto the injectors 22 by way of a leak return passage 23. The system 10 iscontrolled via an electronic controller, or control unit (ECU), 18. TheECU 18 is connected to an electrical actuator 28 of the pump 16 via acontrol communication line 29 and also connected to each injector 22 viafurther communication lines (not shown). When in operation, controlsignals from the ECU 18 control when and how much fuel from the pump 16is fed into the common rail 20, as well as when and for how long theinjectors 22 inject fuel.

FIGS. 2 and 3 show that the pump 16 includes a high pressure outlet 30fluidly connected to the high pressure rail 20 and an inlet 33 fluidlyconnected to the fuel transfer pump 14. A supply passage 43 connects theinlet 33 with first and second pumping chambers 46,56. The pump 16 alsoincludes a first plunger 45 adapted for reciprocating movement in thefirst pumping chamber 46 in a first barrel 44. Furthermore, the pump 16includes a second plunger 55 adapted for reciprocating movement in thesecond pumping chamber 56 in a second barrel 54. The first and secondbarrels are preferably formed in a common pump housing 40. A pair ofcams 34 and 35 are operable to cause the plungers to reciprocate out ofphase with one another. In the illustrated embodiment, the cams 34,35each have three lobes such that one of the plungers 45,55 is undergoinga pumping stroke at about the time that one of the fuel injectors 22 isinjecting fuel. Thus, the cams 34,35 are preferably driven to rotatedirectly by the engine at a rate that preferably synchronizes pumpingactivity to fuel injection activity in a conventional manner.

When the first plunger 45 is undergoing its retracting stroke, fresh lowpressure fuel is drawn into pumping chamber 46 past a first inlet checkvalve 48 from a low pressure area, or gallery, 37 fluidly connected tothe inlet 33. Similarly, when the second plunger 55 is undergoing itsretracting stroke, fresh low pressure fuel is drawn into the secondpumping chamber 56 past a second inlet check valve 58 from the gallery37. When the first plunger 45 is undergoing its pumping stroke, fuel isdisplaced from the pumping chamber 46 either into the low pressuregallery 37 via a first portion 41 of a spill passage and spill controlvalve 38, or into a high pressure gallery 39 past a first outlet checkvalve 47. Similarly, when the second plunger 55 is undergoing itspumping stroke, fuel is displaced from the second pumping chamber 56either into the low pressure gallery 37 via a second portion 51 of aspill passage and spill control valve 38, or into the high pressuregallery 39 past a second outlet check valve 57.

Referring in particular to FIG. 4, only one of the pumping chambers46,56 is fluidly connected to spill control valve 38 at any one time.These fluid connections are controlled by a shuttle valve 80 whichincludes a ball valve member 81. The ball valve member 81 is exposed tofluid pressure in both the first and second pumping chambers 46,56.Because the plungers 45,55 are out of phase with one another, onepumping chamber will be at low pressure (retracting) when the otherpumping chamber is at high pressure (advancing) and vice versa. Thisaction is exploited to move the ball valve member 81 back and forth toconnect either first spill passage 41 to the spill control valve 38, orthe second spill passage 51 to the spill control valve 38. Dependent onits position, the ball valve 81 defines a portion of either the first orsecond spill passage 41,51 which allows the pumping chambers 46,56 toshare a common control valve 38. When the first plunger 45 is undergoingits pumping stroke, the second pumping chamber 56 is refilled past thesecond inlet check valve 58. When the second plunger 55 is undergoingits pumping stroke, the first pumping chamber 46 is refilled past thefirst inlet check valve 48.

The spill control valve 38 includes a spill valve member 60 thatincludes a closing hydraulic surface 62. The spill valve member 60 isnormally biased downward towards its open position via a biasing means,here represented by a biasing spring 64. The valve member 60 rests upona valve stop 63 when in its open position. The spill valve member 60 canbe moved upward to close by energizing an electrical actuator 28. In theillustrated embodiment, the actuator 28 is a solenoid having an armature36 adapted to move the spill valve member 60. That said, those skilledin the art will appreciate that the actuator 28 could take a variety offorms, including piezo and/or piezo bender actuators.

FIG. 5 is a chart illustrating the operation and control of the spillcontrol valve 38 over one complete rotation of the pump camshaft, i.e.the rotation of the camshaft over 360 degrees. The ECU 18 monitors therotational position of the camshaft and also the angle of specific camsvia sensors (not shown). The signals generated by the sensors allow theECU to accurately determine when a specific plunger 45,55 is at itsbottom dead center (BDC) position. Lines A and B in the FIG. 5 chartillustrate the movement of the first and second plungers, respectively,under the action of the first and second cams 34,35, over a singlerotation of the camshaft. As the pump 16 has two plungers 45,55 and eachof the cams 34,35 has three lobes, the pump 16 is able to pump fuel sixtimes for each rotation of the camshaft. The lines C1 and C2 illustratefirst and second control signals, respectively, fed to the spill controlvalve 38 via the actuator 28 during the operation of the pump. The firstcontrol signal C1 pulls the spill valve member into a closed positionagainst the biasing force of the valve spring, while the second controlsignal C2 acts against the bias of the spring to decelerate the openingvalve and reduce the impact of the valve member on the valve seat. Thechart of FIG. 5 also shows the dwell D between the first and secondsignals C1,C2 and also the dwell d between the second signal C2 and thefirst signal C1 of the subsequent pumping event.

INDUSTRIAL APPLICABILITY

The present device and method may be used in any fluid system wherethere is a desire to control discharge using a pump having reduced valvewear and damage. In particular, the present device and method may beused with common rail fuel injection systems. However, those skilled inthe art will appreciate that the present device and method may also beused in other hydraulic systems that may or may not be associated withan internal combustion engine.

Referring to FIG. 1, when the fuel system 10 is in operation, the firstand second cams 34,35 rotate, causing the plungers 45,55 to reciprocatein their respective barrels 44,54 out of phase with one another. Whenthe first plunger 45 is undergoing its pumping stroke, second plunger 55will be undergoing its retracting stroke. This action is exploited viaball valve 80 to either connect the first pumping chamber 46 or thesecond pumping chamber 56 to the spill control valve 38. As one of theplungers begins its pumping stroke, fuel is initially displaced from thepumping chamber through spill control valve 38 to the low pressuregallery 37. When there is a desire to output high pressure from thepump, electrical actuator 28 is energized to close spill control valve38. The first control signal C1 lasts for a first period of timeextending from a first time point occurring after one of the plungerspasses bottom dead center (BDC) to a second time point occurring beforethe plunger passes top dead center (TDC). During this first time period,the spill valve member is closed and then is stopped at the second timepoint as the increased pressure in the pumping chamber is sufficient tohold the valve member 60 closed against the bias of the valve spring 64.In the dwell D between the first and second control signals C1,C2, theadvancing stroke of the plunger continues to compress the fuel in thepumping chamber until it reaches a sufficient pressure to be pushed pastthe respective check valve 47,57 into the high pressure gallery 39 andinto the common rail 20.

As the pressurized fuel is discharged through one of the check valves47,57, the pressure in the pumping chamber 46,56 rapidly drops. As aresult, the forces on the valve member 60 are now unbalanced, with theforce of the valve spring 64 outweighing the hydraulic forces on thelifting surface 62 of the valve member 60. The second control signal C2is generated for a second period of time extending from a third timepoint occurring after the second time point (the end of first controlsignal C1) but before the passing of the plunger through TDC, to afourth time point occurring after the plunger has passed TDC. In thisway, the second control signal C2 is generated just as the pressurizedfuel is discharged from the pumping chamber. The purpose of the secondcontrol signal C2 is to partially counter the force of the spring 64. Inthis way, the second control signal C2 decelerates the valve member asit returns towards the open position, ensuring that the impact of thevalve member 60 on its valve stop 63 is significantly reduced comparedwith conventional arrangements in which the valve returns to the openposition unchecked under the force of the spring 64.

It will be appreciated that the timing of the control signals, and thefirst control signal C1 in particular, determines what fraction of fueldisplaced by the plungers enters the high pressure gallery 39 and whatfraction returns to the low pressure gallery 37. This operation ensuresthat the pressure can be maintained and controlled in the common rail.While one plunger is advancing (pumping), the other plunger isretracting and drawing low pressure fuel into its pumping chamber pastone of the respective inlet check valves 48,58.

By generating a second control signal, the pump of the present inventionensures that wear and damage on the control valve member is reducedcompared with previous proposals for variable discharge pumps. This willensure that maintenance and replacement of pumps according to thepresent invention will be less than at present, with associated costsavings for users of such pumps. In addition, with less wear and damageon the valve member, the performance of the pump will be more consistentover its operating life than is the case at the moment.

It will be understood by those skilled in the art that the duration ofthe second control signal C2, i.e. the position of the fourth timepoint, and the dwell d between the end of the second control signal C2and the beginning of the subsequent first control signal C1, can bevaried by the ECU. The ECU can be provided with a receiving means whichallows the ECU to receive data relating to fluid pressurizationparameters from an external device, e.g. an engine speed sensor on aninternal combustion engine. In addition, reference data relating tofluid pressurization parameters can be stored either by the ECU or by adata storage device connected to the ECU. This allows the ECU to varythe fourth time point for particular engine speeds (received data) anddesired rail pressures (stored data). In addition, the ECU can vary thedwell d depending on data received for the external device.

Although the preferred embodiment of the pump described above comprisesa pair of pumping chambers with associated plungers and plunger bores,it will be understood that the present invention could be provided withonly a single pumping chamber with an associated plunger and plungerbore if desired.

Additionally, although the preferred embodiment of the present inventiondescribed above includes a single spill control valve opening andclosing fluid communication between the pumping chambers and the lowpressure area, the present invention may be modified to include a secondspill control valve. In such an arrangement, the present inventionincludes first and second control valves opening and closing fluidcommunication between their respective first and second pumping chambersand the low pressure area. The controller is consequently adapted tooperate each of the first and second control valves for first and secondtime periods dictated by the reciprocating movements of the respectivefirst and second plungers, in the manner described above.

These and other modifications and improvements may be incorporatedwithout departing from the scope of the present invention.

1. A pump comprising: a first pumping chamber; a first reciprocatingplunger disposed within a first plunger bore so as to reciprocate withinthe first pumping chamber; a first electrically actuated spill controlvalve adapted to open or close fluid communication between the firstpumping chamber and a low pressure area; and a controller adapted tooperate the first control valve for a first period of time extendingfrom a first time point occurring after the first plunger passes bottomdead center to a second time point occurring before the first plungerpasses top dead center; and the controller being adapted to operate thefirst control valve for a second period of time extending from a thirdtime point occurring between the second time point and the passing ofthe first plunger through top dead center to a fourth time pointoccurring after the first plunger has passed top dead center.
 2. Thepump according to claim 1, wherein the first control valve is a solenoidvalve.
 3. The pump according to claim 1, wherein the controllercomprises an electronic control unit.
 4. The pump according to claim 3,wherein the electronic control unit includes a data storage device whichstores one or more fluid pressure parameters, and wherein the controlunit is adapted to vary the operating of the first control valveaccording to the stored parameters.
 5. The pump according to claim 3,wherein the electronic control unit includes a receiver adapted toreceive data relating to fluid pressure parameters from an externaldevice, and wherein the control unit is adapted to vary the operating ofthe first control valve according to the received signals.
 6. The pumpaccording to claim 1 and including: a second pumping chamber; and asecond reciprocating plunger disposed within a second plunger bore so asto reciprocate within the second pumping chamber; wherein the firstcontrol valve is adapted to open or close fluid communication betweenthe second pumping chamber and the low pressure area; wherein thecontroller is adapted to operate the first control valve for a firstperiod of time extending from the first time point occurring after oneof the plungers passes bottom dead center to the second time pointoccurring before the one of the plungers moves through top dead center;and wherein the controller is adapted to operate the first control valvefor a second period of time extending from the third time pointoccurring between the second time point and the movement of the one ofthe plungers through top dead center to the fourth time point occurringafter the one of the plungers has moved through top dead center.
 7. Thepump according to claim 6, wherein the one of the plungers is the secondplunger.
 8. The pump according to claim 6, wherein the first and secondplungers are adapted so as to reciprocate out of phase with one another.9. The pump according to claim 6 and including: a spill passage fluidlyconnecting the first and second pumping chambers; and a shuttle valvelocated in the spill passage and adapted to be exposed to fluid pressurein the first and second pumping chambers; the shuttle valve including ashuttle valve member moveable between a first position in which thefirst pumping chamber is fluidly connected to the control valve and asecond position in which the second pumping chamber is fluidly connectedto the control valve.
 10. The pump according to claim 9, wherein theshuttle valve is a ball valve and the shuttle valve member is a ball.11. The pump according to claim 6, wherein the first control valve is asolenoid valve.
 12. The pump according to claim 6, wherein thecontroller comprises an electronic control unit.
 13. The pump accordingto claim 12, wherein the electronic control unit includes a data storagedevice which stores one or more fluid pressure parameters, wherein thecontrol unit may vary the operation of the control valve according tothe stored parameters.
 14. The pump according to claim 13, wherein theelectronic control unit includes a receiver adapted to receive datarelating to fluid pressure parameters from an external device, whereinthe control unit may vary the operation of the control valve accordingto the received signals.
 15. The pump according to claim 1 andincluding: a second pumping chamber; a second reciprocating plungerdisposed within a second plunger bore so as to reciprocate within thesecond pumping chamber; and a second electrically actuated spill controlvalve adapted to open or close fluid communication between the secondpumping chamber and the low pressure area; wherein the controller isadapted to operate the second control valve for a first period of timeextending from a first time point occurring after the second plungerpasses bottom dead center a second time point occurring before thesecond plunger moves through top dead center; and wherein the controlleris adapted to operate the second control valve for a second period oftime extending from a third time point occurring between the second timepoint and the movement of the second plunger through top dead center toa fourth time point occurring after the second plunger has moved throughtop dead center.
 16. The pump according to claim 15, wherein the firstand second plungers are adapted so as to reciprocate out of phase withone another.
 17. The pump according to claim 15, wherein the firstcontrol valve is a solenoid valve.
 18. The pump according to claim 15,wherein the second control valve is a solenoid valve.
 19. The pumpaccording to claim 15, wherein the controller comprises an electroniccontrol unit.
 20. The pump according to claim 19, wherein the electroniccontrol unit includes a data storage device which stores one or morefluid pressure parameters, wherein the control unit may vary theoperation of the control valve according to the stored parameters. 21.The pump according to claim 19, wherein the electronic control unitincludes a receiver adapted to receive data relating to fluid pressureparameters from an external device, wherein the control unit may varythe operation of the control valve according to the received signals.22. The pump according to claim 15, wherein the first and second controlvalves are actuatable towards a closed position when operated.
 23. Thepump according to claim 15 including first and second springs adapted tobias the first and second control valves, respectively, in the openposition.
 24. An internal combustion engine including a pump accordingto claim
 1. 25. A method of pressurizing fluid in a pump, the methodcomprising the steps of: supplying low pressure fluid to a pumpingchamber; reciprocating a plunger within the pumping chamber so as toforce fluid from the pumping chamber; returning a portion of the fluidfrom the pumping chamber through an electrically actuated spill controlvalve; operating the electrically actuated spill control valve topressurize the fuel in the pumping chamber during a forward stroke ofthe plunger; and discharging the pressurized fuel through a dischargeport in communication with the pumping chamber; wherein the operatingstep includes operating the control valve for two separate periods oftime, a first period of time extending from a first time point occurringafter the plunger passes bottom dead center to a second time pointoccurring before the plunger passes top dead center, and a second periodof time extending from a third time point occurring between the secondtime point and the passing of the plunger through top dead center to afourth time point occurring after the plunger has passed top deadcenter.
 26. The method according to claim 25 and including the step ofreceiving data relating to fluid pressure parameters from an externaldevice, and varying one or both of the first and second periods of timeof the operating step according to the received data.
 27. The methodaccording to claim 26, wherein a dwell time period between the fourthtime point of the operating step and the first time point of asubsequent operating step is varied according to the received data. 28.The method according to claim 26 further comprising the step of storingdata relating to one or more fluid pressure parameters, and varying oneor both of the first and second periods of time of the operating stepaccording to the stored data.
 29. The method according to claim 28,wherein the fourth time point is varied according to the stored data andthe received data.